Reserve Estimation

RESERVE ESTIMA ESTIMATION TION B.B.SHARMA Suptg. Geologist GSI, NER, Shillong

WHAT IS RESERVE? • The Sizing up of ore body is known

as Reserve. • It tells about the quality, quantity

and amenability to commercial exploration of raw material. • It starts from preliminary to last

stage of exploration and mining

ESTIMATION OF RESERVE

Reserve is determined by multiplying the volume of the ore body by the bulk density

Parameters of Reserve Estimation • Cut off grade •

Stopping width

•

Weighted average and average grade

•

Tonnage factors

•

Core recovery

•

Thickness

•

Strike length/strike influence

•

Dip length/width influence

•

Correlation of lode

Tonnage factor 

● Tonnage factor or bulk density is a multiplier to the volume for the determination of reserve. ● This can be determined by following methods ►Cubical opening method ► Conventional density measurement method ► Determination of bulk density using drill cores

Cubical opening method •Dig up a pit of 1mx1mx1m size and weight all the material this weight is tonnage factor. •For sulphide ore deposit at initial exploration this method is not applicable. •In case of iron ore , limestone, rock Phosphate is applicable. •in the mining stage normally bulk density is determined by this method

Conventional density measurement method Density is determined by weighing the sample in the air and in the water by steel yard balance by the following formula. D= W/V W= weight V= volume D= W1/W1-W2 W1=weight in the air W2=weight in the water

Bulk density using drill cores The bulk density can be determined by this method by measuring the length of the core or half split core V= πR²l (if the core is not split) V=1/2πR²l (if the core is half split) V= Volume R= Radius of core sample l= Length of core sample Weight the measured core and determine the bulk density by DB=M/V

Core Recovery ● Core recovery plays important role in computation of reserve estimation core recovery should be very high at least in mineralized zone. ►Core recovery in the lode is more than 95% then for the reserve calculation it may be taken as 100%. ►Core recovery is less than 95% then correction factors have to be applied.

Dilution method: ● In this method the assay value of recovered core is distributed in the whole run assuming that the part of core which is not recovered is barren by this method grade will go down the assay value.

Reduced width method: ● In this case core loss is considered as voids and the lode width is taken as the length of the core recovered. Thus the thickness of lode will reduced however the grade will be as per the assay value.

Equal grade method: ●The core recovery is > 95%.

The recovered length is taken as the grade of run with the assumption that the uncovered portion also contains same assay value. ●

Thickness ●Thickness of the ore body is measured by computing the thickness of the load in individual hole for which the true thickness is needed. ►Oblique borehole to the ore body gives apparent thickness which needs correction for revealing the true thickness.

Thickness -- A) Azimuth and Zenith Perpendicular to strike and Dip plane -No

correction is needed.

B) Azimuth Perpendicular to the Strike and Zenith oblique to the Dip plane 1.If borehole is vertical Tr=Tv x Cosα=Th x Sinα 2.If borehole is inclined Tr=Ti x Sinβ

Thickness Thickness of the body is determined by computing the thickness of the lode in individual hole, RL in meter

Bore hole

True thickness (Tr) 

 Apparent Thickness (Ta)

Lode

Distance in Meter

Tr = Ta * sin Tr = True thickness Ta = Apparent thickness = Angle between core axis and bedding plane

Thickness --C) Azimuth and Zenith Oblique to the Strike and

Dip plane Tr= Tap x cosβ cosθ (cosα tanβ+tanθ) or = Tap(cosα sinβ cosθ+cosβ sinθ) Th= Tap(cosα cosθ+ tanβ sinθ) Tv= Tap cosθ(cosα tanβ+tanθ) α- angle bet the plane of the dip and the plane of the hole direction β- Dip of the ore body θ- Angle of the hole intersected in the borehole

Strike length/ strike influence ●The strike length is determined on the basis of opening along the strike of the ore body. ●The strike influence of each opening is determined on the basis of nearest point and gradual variation. ● In case of correlate able lode the strike influence is taken as half the distance between two opening. ●In non-correlateable lode also the distance along strike is taken as half the distance between two points or less than that depending upon the variation of the ore body

Strike length

500m

N

X-3

N

Distance

300m

Bore hole

X-2

Dolomite

Lode

X-1 100m Distance

E

Geological map

Schist

 N

SURFACE GEOLOGICAL MAP OF BLOCK ‘A’

 N

0m

20 m

Scale (1:1000)

BH-1 BH-2 0

500 m

0

0

0

X-3

0

X-2

400 m

  m   n    i   e   c   n   a    t   s    i    D

300 m

0

0

0

BH-3

BH-4

0

200 m INDEX

100 m

W

0

0 0

BH-5 BH-6 0

0

X-1

E

00 m S

50

100

150

200

250 m

Distance in m

Dip Length/ Dip Influence ► As strike influence the dip length influence, for each opening is also taken as half the distance between the adjacent opening in the case of inclined ore body, if the ore body have been intersected at different level. ► For the computation of the reserve of each opening the volume is determined by multiplying the strike influence with dip length influence and thickness intersected.

Geological cross section along Line –  X1 W

E

BH-3

BH-4

350 m

RL 300 m

Po RL

250 m

Pr

200 m

RL 150 m

Pr 100 m

RL Po

50 m

Inf 0m 50 m

100 m

150 m

200 m

250 m

300 m

ORE RESERVE CALCULATION METHODS For homogeneous bedded horizontal or low dipping deposits 

Included area method



Extended area method



Triangle method



Polygon method



Method of isoline



Isopach maps method

For moderately to steeply dipping tabular ore body 

Cross section method



Longitudinal section method



Level plan method

Cross section method  The

cross-section or traverse  section prepared across the ore body represent the actual geological features in shape and quality

 For

the calculation of the reserve by this method the area of influence and quality is considered on the basis of the rule of nearest point

 In

the cross  section area method the reserve is calculated for individual opening and the area of influence of that opening is measured on the cross section or calculated by measuring actual thickness and dip length. Bore hole 1

RL in mt.

Bore hole 2

188 180 171 164

Lode Dolomite

Distance in Meter B h N o .

1

App. Thickne ss

12m

Angle of lode with core axis

78⁰

True thickness

11.5

Core recovery

100%

%Cu

2

Lode RL

Dip Length

Upper

Lower

180m

171m

31

Dip RL

Upper

Lower

188m

164m

Strike length

Tonnage factor

categor  y

Tonnage T*DL*SL*TF in tonnes

200m

2.5

Probabl e

186000

Total reserve

Longitudinal vertical projected section method   



This method is very helpful in correlating the ore body along the strike This method is very useful in determining the reserve of complex ore body like tabular and ore shoot body. In longitudinal vertical projected section the RL of the intersection of the ore body is projected on any vertical plane parallel to the strike of the ore body and lodes are correlated. In this area of influence is taken half the distance between openings and that is measured on the section or computed by multiplying the X and Y.

X-1 500

RL in mt.

BH1

BH2

100

X-2

X-3

Level plan method Level plan is prepared by plotting of the lode intersection on a horizontal plan passing through the level of intersection or at particular RL. It represents the lode at that particular level. BH1

BH2

X-3

BH3

300m

BH4

Bore hole

X-2

Dolomite

Lode

Schist

BH5

X-1 100m Distance

Geological map

E

BH6

Cross section X-1

X-2 BH5

X-3 BH3

BH6

RL

BH1

BH4

RL

RL

Soda Rhy.

160m

DolomiteLode

Distance

Distance

Distance

Level plan at 160m RL X-3

N

Distance

300m

X-2

Dolomite

X-1 100m

Lode

Soda rhy.

BH2

EXERCISE